Almost all goods manufactured and/or consumed in industrialized nations are loaded on and transported by railroad cars or trucks at one point during their distribution. Accordingly, the number of freight-carrying railroad cars and trucks and, in particular, semi-trailers is in the millions, representing investments of many billions of dollars.
The present invention is directed to improvements in the construction of such vehicles. For purposes of this application and the claims appended hereto the term "vehicle" means and is intended to include truck trailers (both semi-trailers and trailers having forward and aft axles), all types of railroad freight cars (such as boxcars, gondola cars, flat cars, refrigerator cars and the like) and similar vehicles intended to haul heavy loads, normally amounting to many tons at relatively high speeds over long distances, whether on roadbeds, rails, or other support surfaces (hereinafter sometimes collectively referred to as "support surfaces").
The outer appearances of such vehicles may vary widely in terms of their size, load carrying capacity, shape and intended use. Structurally, however, they are relatively similar. Generally, each such load carrying vehicle comprises an axle assembly, in the form of a pair of railroad truck assemblies for a railroad car, forward and aft axle assemblies for trailers, or a kingpin-saddle plate arrangement combined with an aft axle assembly for semi-trailers, together with a load supporting underframe mounted on top thereof to define or to carry means defining the load carrying surface. In addition, the vehicle may have front and aft bulkheads (railroad flat cars; flat bed trailers), side and end walls (railroad gondola cars, trailers) and a roof (railroad boxcars, trucks, trailers, or semi-trailers). The side walls, end walls and the roof normally do not have a load carrying capacity (other than an ability to withstand wind forces, snow loads, etc.) and are constructed relatively light, normally no stronger than is necessary to withstand the forces to which they are subjected during normal use while assuring the desired holding and/or protecting characteristics for the load carried by the vehicle.
Aside from the wheel or truck assemblies the underframe is the most important load supporting structure. It is here that a major portion of the expense of prior art vehicles of the type discussed above is incurred. Generally speaking, the underframe comprises one or more longitudinally running beams, normally arranged close to the center of the car and, projecting therefrom, a multitude of cantilevered arms, beams, plates and the like, all of which are intricately shaped and individually secured, e.g. welded or bolted to the main beam or beams. Such frames are constructed of literally hundreds of individual parts which must be individually formed, e.g. cut, stamped, bent and the like and which must thereafter be individually hand-welded to the main beam. The main beam itself is intricately shaped, frequently it is tapered so as to prevent them from interfering with the wheel assemblies, to minimize its weight and enable it to carry a maximum payload. The penalty for such a construction, however, is a great deal of costly labor which correspondingly increases the cost of the finished vehicle.
The following U.S. Patents are representative of the above-discussed overall construction of such vehicles: U.S. Pat. Nos. 2,172,571; 3,055,317; 3,185,112; and 4,049,285. The patents illustrate various attempts to construct the underframe for such vehicles. In all instances, except for the last mentioned patent, it requires the assembly of a multitude of parts. In the last mentioned patent the large number of parts is replaced with intricate, extruded aluminum floorboards which, it is believed, would not only be costly to make but would additionally be unsuited for heavy duty use as is ecountered in many truck applications and in connection with virtually all railroad applications.
Common to these prior art structures, however, is the provision of main, usually centrally located, longitudinally running support beams from which lateral extensions protrude. Thus, another characteristic for these structures is that cross-section of the underframe, in a direction perpendicular to its length, is greatest in the vicinity of the beams, normally adjacent the longitudinal center of the frame and least at the outer edges of the frame. The reason for this construction is that the ultimate weight supporting member, the longitudinally running beams, do not span the entire width of the frame and that cantilevered structures are attached to these beams to extend their effectiveness over the full width of the load carrying surface.